1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor, a method for producing the same and electrophotographic apparatus, and more particularly to an electrophotographic photoreceptor suitable for producing good images even in printing under high humidity, a method for producing the same and electrophotographic apparatus.
2. Description of the Prior Art
As electrophotographic photoreceptors, there are conventionally used inorganic photoconductors such as Se, CdS, As.sub.2 Se.sub.3, etc. and organic photoconductors represented by phthalocyanine pigments. These materials are superior in electrophotographic characteristics such as photosensitivity, charge acceptance, etc., but as to mechanical characteristics, have defects that the film hardness is low and the abrasion resistance is poor.
Contrary to this, amorphous silicon photoreceptors have a high hardness and excellent abrasion resistance, so that they are expected as long-life electrophotographic photoreceptors.
The amorphous silicon photoreceptors, however, have a defect of the humidity resistance being poor. Because of this, providing the photoreceptors with a surface protective layer made of a-SiC:H, a-SiN:H, etc. is commonly carried out, but it may not be said to be satisfactory.
Also, the printing process of electrophotography includes a charging process by corona discharge, so that repeating the printing process causes oxidation of the surface protective layer and lowering of the humidity resistance to result in a defect of image blurring occurring.
In order to overcome such a defect of photoreceptors, there are many proposals on various surface protective layers.
For example, Japanese Patent Application Kokai No. 55-84941 and No. 55-70848 disclose to provide the photoreceptors with a surface layer made of thermosetting resins or thermoplastic resins.
Also, Japanese Patent Application Kokai No. 56-51754 and Japanese Patent Application Kokai No. 58-23031 and No. 58-102949 disclose to provide the photoreceptors with a surface layer in which solid particles of polytetrafluoroethylene, etc. have been dispersed as a lubricant in thermoplastic resins or insulating resins.
Further, Japanese Patent Application Kokai No. 57-165848 discloses a surface layer in which an inorganic insulator has been dispersed in insulating resins. And, Japanese Patent Application Kokai No. 56-99347 and No. 57-165848 disclose a surface layer in which a lubricant and an abrasive such as alumina have been dispersed in resins.
Further, U.S. Pat. No. 3,954,466 is mentioned as a description of the prior art.
However, the surface protective layers of these conventional techniques have a problem of failing to fully satisfy all of the various characteristics required for the surface protective layer such as for example durability for corona irradiation, polishing abrasion resistance to paper, cleaning brushes, etc., cleaning characteristics at the time of removal of toners, prevention of a toner adhesion problem, etc. "Toner adhesion problem" referred to herein means a problem that a thermoplastic resin, etc. contained in broken pieces of a toner adheres to a photoreceptor in an aggregated or molten state never to be removed therefrom.
For example, the surface layer composed of a resin alone is in sufficient in the abrasion resistance when its film thickness is so small as not to affect the characteristics of photoreceptors.
When the surface layer is formed by dispersing particles of a solid lubricant such as polytetrafluoroethylene, etc. in a resin, an improvement in lubricity can be expected. However, the film strength lowers at the same time, so that the result is that there remains a problem of the abrasion resistance and durability being injured.
When particles of alumina, etc. are added in order to prevent a lowering in film strength, the lowering in lubricity is brought about unless particle size and particle concentration are made optimum, which results in problems such as lowering in the cleaning characteristics, toner adhesion problem, etc. The result is therefore that there remains a problem of failing to obtain characteristics expected of the surface protective layer.